AL3 Histology of Endocrine Glands

• Pituitary gland


  Small, bean-shaped gland located inferior to the hypothalamus, separated by the diaphragma sellae
• Pituitary gland

  • Divided into three regions: pars distalis, pars tuberalis, and pars intermedia
  • Contains different cell types: chromophobe, basophil, acidophil
• Pars intermedia

  Located between the pars distalis and pars nervosa, contains cuboidal follicular cells and colloid cysts called Rathke cysts
• Pars nervosa

  Main body of the neurohypophysis, contains fenestrated capillary plexus, pituicytes, and axons/axon terminal endings from hypothalamus neurons
• Neurosecretory hormones

  ADH/vasopressin, oxytocin, and neurophysins
• Thyroid gland

  Derived from the developing endoderm of the foramen cecum of the tongue, has two lobes
• Thyroid follicles

  • Main functional components, synthesize and release T3 and T4
  • Filled with colloid, a gelatinous substance containing stored T3 and T4
  • Follicular cells can change from cuboidal to squamous (inactive) or columnar (active) depending on secretion state
• Parafollicular cells (C cells)

  Located between the follicles, produce calcitonin hormone which decreases blood calcium levels
• Graves disease is an example of hyperthyroidism, Hashimoto thyroiditis is an example of hypothyroidism
• Parathyroid glands


  • Typically four small glands, developed from 3rd and 4th pharyngeal pouches, lying posterior to the thyroid gland
  • Consist of chief cells that produce parathormone (PTH) and oxyphil cells with unknown function
• Chief cells

  Principal cells of parathyroid, produce PTH which promotes osteoclast activity and inhibits osteoblast activity
• Oxyphil cells

  Large cells with acidophilic cytoplasm, appear at puberty and increase with age, function unknown
• Adrenal gland

  • Also known as suprarenal gland, covers the apical region of each kidney, has an outer cortex and inner medulla
  • Cortex derived from mesoderm, contains zona glomerulosa, zona fasciculata, and zona reticularis
  • Medulla derived from neural crest, contains sympathetic ganglion neurons and chromaffin cells that produce adrenaline and noradrenaline
• Adrenal gland

  • Covers the apical region of each kidney
  • Has an outer cortex and inner medulla
  • Covered by a connective tissue capsule
• Adrenal cortex

  Derived from the mesoderm<|>Divided into 3 zones: zona glomerulosa, zona fasciculata, and zona reticularis<|>Hormone-producing cells secrete mineralocorticoids, glucocorticoids, and weak androgens
• Adrenal medulla

  Derived from the neural crest<|>Contains cell bodies of sympathetic ganglion neurons and their axons<|>Contains chromaffin cells that synthesize and release adrenaline and noradrenaline
• Adrenal cortex

  • Contains many glandular cells arranged in cords
  • Capillaries run parallel to these cords
• Zona glomerulosa

  • Lies beneath the connective capsule
  • Secretory cells contain lipid droplets and pale-staining cytoplasm
  • Arranged in round or ovoid clusters
  • Secrete mineralocorticoids, mainly aldosterone
• Zona fasciculata

  • Contains hormone-secreting cells that secrete glucocorticoids (mainly cortisol and corticosterone)
  • Cells contain many lipid droplets, making the cytoplasm appear light and vacuolated
  • Cells are arranged in long cords with nuclei packed close to capillaries
• Zona reticularis

  • Adjacent to the medulla
  • Secretory cells contain few lipid droplets and have dark, acidophilic cytoplasm
  • Cells are arranged in anastomosing cords intermixed with capillaries
  • Secrete androgens (mainly dehydroepiandrosterone)
• There are many blood vessels separating the zona reticularis of the cortex and the medulla
• Cells of the adrenal cortex have an abundance of smooth endoplasmic reticulum, mitochondria with tubular cristae, and lipid droplets
• Cholesterol, the precursor of steroid hormones, is stored as esters in the lipid droplets
• Adrenal medulla cells

  Synthesize and secrete adrenaline (epinephrine) and noradrenaline (norepinephrine), with adrenaline being the main product
• Catecholamines

  Synthesized from the amino acid tyrosine through a series of reactions in the cytosol and within the granules in the cytoplasm
• Pineal gland


  • Pine cone-shaped neuroendocrine gland about 8 mm in length
  • Produces melatonin
  • Covered by a capsule of pia mater
  • Part of the epithalamus that extends caudally from the posterior commissure
• Melatonin secretion

  Stimulated by darkness and inhibited by light<|>Increases during sleep
• Pineal gland contents

  • Pinealocytes
  • Neuroglial cells
  • Blood vessels
• Pinealocytes


  Modified neurons with round or ovoid nuclei and pale-stained cytoplasm containing melatonin granules<|>Synthesize melatonin, important in regulating circadian rhythms<|>Have long cytoplasmic processes extending to capillaries
• Neuroglial cells

  Supportive cells with small, dark nuclei<|>Also called pineal astrocytes<|>Commonly found near capillaries
• Other functions of the pineal gland may relate to promoting sleep, enhancing mood, slowing aging, and inhibiting tumor growth
• Calcified concretions called brain sand may be present in the pineal gland, especially in older patients
• Pancreas


  98% exocrine (compound tubule-acinar type)<|>2% endocrine (islets of Langerhans)<|>Islets more numerous in the tail part of the pancreas
• Islets of Langerhans

  • Clusters of endocrine cells within a capillary network
  • Surrounded by eosinophilic exocrine component
  • Divided by connective tissue septa
• Endocrine pancreas


  Does not have ducts<|>Hormones (insulin and glucagon) secreted by islets are released into the capillaries and blood circulation
• Endocrine cell types in islets of Langerhans

  • Alpha cells
  • Beta cells
  • Delta cells
  • PP cells
• Alpha cells

  Secrete glucagon, which acts on the liver to raise glucose levels
• Beta cells

  Secrete insulin, which acts on the liver, muscle, fibroblasts, and adipocytes to increase glucose uptake
• Delta cells


  Secrete gastrin and somatostatin, which inhibit insulin and glucagon secretion
• PP cells


  Produce pancreatic polypeptide